The present invention relates, in general, to high frequency transistors, and more particularly, to a transistor structure that increases the high frequency stability and gain of the transistor.
Gallium Arsenide (GaAs) metal semiconductor field effect transistors (MESFETs) have been used in the industry for various applications including high frequency amplifiers that had low noise and high gain, and power amplifiers. Previous methods for implementing these MESFETs produced parasitic components that were detrimental to high frequency operation of the MESFET and limited the performance of amplifiers that used the MESFETs. The parasitic components made the MESFET unstable thereby creating oscillations in amplifiers using the MESFET. Previous methods to eliminate or reduce the oscillations involved connecting passive components that were lossy to the MESFETs. For example, a capacitor or inductor that exhibited resistive behavior at high frequencies may have been added to offset the effects of the parasitic components of the MESFET and make the amplifier more stable. Although these lossy components made the amplifier more stable, the lossy components dissipated power thereby reducing the power output of the amplifier and also reducing the gain of the amplifier. Since the noise figure of an amplifier is a function of the gain of the amplifier, the lossy components also increased the noise figure of the amplifier thereby reducing the effectiveness of the amplifier.
Accordingly, it would be desirable to have a MESFET that is more stable at high frequencies and also has more gain at those frequencies thereby eliminating the use of lossy components in some amplifiers and reducing the number of components used in others.